TAILOR-PCI is a multi-site, open label, prospective, randomized trial testing the hypothesis that after percutaneous coronary intervention (PCI), using a genotyping strategy ticagrelor 90 mg twice per day is superior to clopidogrel 75 mg per day in reducing a composite endpoint of major adverse cardiovascular events (MACE), i.e., non-fatal myocardial infarction, non-fatal stroke, severe recurrent ischemia, cardiovascular (CV) death, and stent thrombosis (primary endpoints) in CYP2C19 reduced function allele patients. Patients who undergo PCI will be randomized to a conventional therapy arm (i.e., to receive clopidogrel 75 mg once daily without prospective genotyping guidance) versus a prospective CYP2C19 genotype-based anti-platelet therapy approach (ticagrelor 90 mg bid in CYP2C19 *2 or *3 reduced function allele patients, clopidogrel 75 mg once daily in non-*2 or -*3 CYP2C19 patients). Buccal swabs will be obtained for those subjects randomized to the prospective genotyping arm. All subjects will have a blood sample drawn for DNA analysis but genotyping using these DNA samples will be performed only after completion of the duration of anti-platelet therapy (i.e., after one year). The primary endpoints will be assessed prospectively and will be compared between the conventional arm and the prospective genotyping arm among those identified as reduced function CYP2C19 allele carriers according to the 1-year genotype results.